An industrial robot is commonly used in the industry. FIG. 10 illustrates a schematic industrial robot 100 comprising a controller 101 including a calculator 102, manipulator 103 and a robot controller. As an example for origin adjustment in a conventional industrial robot, Japanese Patent Unexamined Publication No. H02-180580 (document 1) discloses the following device. FIG. 8 illustrates a conventional origin adjusting device.
The conventional origin adjusting device shown in FIG. 8 has first member 81 and second member 82 arranged facing each other. The circumferential surface of first member 81 is provided with step 83 at a position corresponding to an origin, and second member 82 detachably fixes an origin adjusting device at a position corresponding to an origin. This origin adjusting device is composed of switch holder 85, fixed to second member 82 at a position corresponding to an origin; switching means 84 for transmitting an origin signal, held by switch holder 85; and sliding stick 87. One end of sliding stick 87 is able to engage an on-off movable element of switching means 84, and the other end is able to project toward the inside of step 83 formed at an origin-corresponding position of first member 81, guided by direct-acting bearing 86 fixed to switch holder 85.
Meanwhile, as another example for a conventional industrial robot performing origin adjustment, Japanese Patent Unexamined Publication No. 2002-239967 (document 2) illustrates an origin adjusting device as shown in FIG. 9.
The origin adjusting device shown in FIG. 9 is provided with first member 91 and second member 92 facing each other and being relatively rotatable. First member 91 is provided with attaching part 95 for detachably attaching positioning member 94. Second member 92 is provided with contacting surface 93 contacting positioning member 94. Positioning member 94 is threaded, pin-shaped, and attaching part 95 is a screw hole screwable together with positioning member 94.
However, in the makeup shown in document 1, the origin adjusting device, being detachable, requires the trouble to be prepared when origin adjustment is needed. Further, dust prevention measures need to be taken for the attaching part of the origin adjusting device because the robot body can gradually become dirty in a field. Additionally, the complicated makeup causes the origin adjusting device and the joint member of the robot to be expensive.
Installing an origin adjusting device requires a relatively large space, thus making downsizing of the robot joint difficult. Particularly at the end-effector attaching part of the robot and the wrist shaft, which is located near the attaching part, the leading end of the wrist shaft is prevented from accessing a workpiece, which is extremely disadvantageous makeup.
Meanwhile, in the makeup of document 2, although the origin adjusting device is inexpensive, the positioning member is screwed in a screw hole, and thus the fixing accuracy of the positioning member results in being dependent on the coaxialities of the thread-processed part and pin-processed part, which will bring poor positioning accuracy.
Even if some objects are produced on the basis of an identical design drawing, strictly speaking, they individually differ in dimensions due to unevenness in production and/or processing. An object with an identical shape but slightly different dimensions is referred to as “a different object belonging to a same kind.” Using such an object causes deterioration in positioning accuracy, disabling stable accuracy in origin adjustment to be secured.